In oil and gas drilling industry, the downhole motor (“mud motor”) is normally disposed between the end of the drill string and the drill bit. When drilling mud is pumped down the drill string from the surface, the mud motor rotates the drill bit allowing it to cut through the surrounding material. Downhole motors are particularly useful in directional drilling, which requires steering the drill bit in a desired direction.
A typical downhole motor includes a rotating shaft (“rotor”) disposed within a fixed housing (“stator”). The rotor is helically-shaped and is offset from the helically-shaped elastomeric inner lining of the stator such that when drilling mud is pumped down the drill string, the rotor rotates relative to the stator. The rotor in turn drives a transmission, which converts the eccentric motion of the rotor into circular motion to drive the drill bit.
The elastomeric inner stator liner must not only withstand the mechanical stresses placed upon it by the rotation of the rotor, but must also resist deterioration from exposure to the components of the drilling mud. However, even though mud motors have been used in the oil and gas drilling industry for many years, the ability to formulate a high-performance stator compound for fabricating the stator lining has proven to be a significant challenge, particularly for stator linings used in high-stress environments, such as those encountered in shale oil drilling operations,
Previous attempts have been made to use NBR copolymers in stator compounds; however, the resulting stator liners provided poor dynamic performance, were subject to high swell in diesel-based drilling muds, and had lower tear and flex fatigue resistance at elevated temperatures (e.g., 200-350° F.).